In double-container systems for receiving and transporting radioactive materials, the two containers disposed one inside the other must fulfill different requirements. The outer shielding container conventionally has a wall thickness of 200 mm in order to provide the necessary shielding against radioactive radiation. Furthermore, this thick-walled outer shielding container is intended to provide mechanical protection of the inside container during transport and when subjected to impact loading.
The inner container receives the radioactive materials and holds them in a gas-tight manner. For this reason, the inner container can be provided with a double-cover system wherein the inner primary cover is threadably fastened to the vessel of the container and provides a gas-tight seal via appropriate seals. An outer secondary cover is welded to the vessel of the storage container where the latter is loaded or at another location.
For closing the loading opening of the outer shielding container which receives the inner storage container, it has been suggested that a closure cover be attached to the end face via machine bolts. This has the disadvantage that the weight of the inner storage container must be transmitted via the machine bolts in the event of an impact loading applied to the double-container unit.
A further suggestion provides that the shielding closure cover of the shielding container be provided with an outer thread and be screwed into the loading opening which is provided with a corresponding inner thread in the upper region thereof. This technical solution has the disadvantage that it is necessary to rotate the entire closure cover or the container for opening or closing. This requires an appropriate technical effort which complicates the nuclear facility because of the very great weight of the shielding cover and shielding vessel of the shielding container. The appropriate specialized means for assisting in this matter must then be made available at all locations.